232 ACIDS. 



For the separation of malic acid, see 214. 



221. Fumaric acid can also be sublimed, and, like oxalic and 

 succinic acids, yields a precipitate with acetate of lead that 

 gradually assumes a crystalline condition ( 81, 214). It 

 differs from malic acid in its slight solubility in water (according 

 to Lassaigne about 1 in 260 at 17). It is much more easily 

 soluble in hot water, and is also dissolved by ether and by cold 

 spirit. The solubility of the silver-salt is extremely slight ; 

 manganous fumarate is also sparingly soluble in water, but freely 

 in spirit. The acid potassium and acid ammonium salts are not 

 very soluble in water, and scarcely at all in cold 80 per cent, 

 spirit. Lime-water does not precipitate fumaric acid. 



Maleic acid is isomeric with the preceding, and, like it, is op- 

 tically inactive and yields a crystalline lead-salt. It is freely 

 soluble in water, but cannot be sublimed without decomposition. 



Kinic acid may also be mentioned here. It is precipitated by 

 ammoniacal, but not by normal acetate of lead ; and when 

 saturated with milk of lime, yields at first a calcium-salt soluble 

 in water. 



Many other vegetable acids can be separated from kinic acid 

 by precipitation with normal acetate of lead ; the filtrate, after 

 removal of the excess of lead as sulphide, can be freed from 

 sulphuretted hydrogen, boiled with milk of lime, concentrated, 

 and allowed to stand, when a crystalline deposit of kinate of 

 calcium will gradually separate, or more rapidly if spirit is added. 

 The presence of kinic acid in the deposit may be demonstrated 

 by heating with sulphuric acid and black oxide of manganese ; 

 the quinone thus produced is volatile, crystallizes in yellow 

 needles, and can be detected even in traces by its iodine-like 

 odour (167, arbutin). 



Kinic acid and its silver-salt are easily soluble in water. 1 



222. Lactic Acid. Although the occurrence of lactic acid in 

 living plants has not been placed beyond doubt, we must devote 

 a few lines to it here, as it is frequently produced from cart 

 hydrates when vegetable infusions are allowed to stand, and is 

 therefore often met with in plant-analysis. It can be detected by 



1 For rubickloric acid, which occasionally accompanies kinic acid and, like 

 it, is only precipitated by alkaline acetate of lead solution, see Schwarz, 

 Sitzungsber. d. Akad. d. W. in Wien Math. nat. 01. 26, 1852. Rubichloric 

 acid is decomposed with simultaneous separation of green insoluble chlorrubin 

 when its aqueous solution is boiled with dilute hydrochloric acid. 



